Plants annual or perennial herbs, with taproots or more commonly rhizomes. Stems erect to spreading or climbing, angled or winged, unbranched or branched, unarmed, glabrous or pubescent with nonglandular hairs. Leaves alternate, even-pinnately compound with 2–10 leaflets (rarely with an extra lateral leaflet along 1 side), the petiole often expanded or winged, the rachis extended into a conspicuous, unbranched or branched tendril (this poorly developed elsewhere). Stipules leaflike, with a basal outgrowth or lobe of tissue on 1 side, this rounded or more commonly triangular, descending or clasping the stem, the margins otherwise entire or less commonly toothed, the venation mostly inconspicuous, persistent; stipels absent. Leaflets oblong to elliptic or linear, the margins entire, the surfaces glabrous or hairy, pinnately veined or only the midvein visible (often with 3 main veins in L. sylvestris). Inflorescences axillary, racemes or clusters, occasionally reduced to solitary flowers, the bracts 1–3 mm long, shed early, bractlets absent. Calyces 5-lobed, the tube bell-shaped, usually oblique, often somewhat pouched on 1 side at the base, more or less 2-lipped, the lobes subequal or the 3 lower lobes longer than the upper 2, variously shaped, sharply pointed at their tips, glabrous or hairy. Corollas papilionaceous, pink, red, purple, or white (yellow elsewhere), lacking conspicuous, contrasting markings near the base of the banner, the banner with a short, sometimes broad, stalklike base, the expanded portion obovate to nearly circular, notched at the tip, sharply curved or bent backward, the wings narrowly to broadly obovate, shorter than to slightly longer than the banner, usually curved over or around but not fused to the keel, the keel shorter than the wings, boat-shaped, curved upward, mostly tapered to a bluntly or sharply pointed tip. Stamens 10, 9 of the filaments fused and 1 free nearly to the base, all similar in length or in 2 alternating, slightly shorter and longer series, the free portions of the filaments slender, but usually broadened toward their tips, the anthers small, attached at the base, all similar in size, yellow or occasionally orange. Ovary sessile or very short-stalked, glabrous or occasionally hairy, the style abruptly curved or bent upward toward the base, somewhat flattened, hairy on the inner surface toward the tip, more or less persistent at fruiting, the stigma terminal, short or somewhat elongate. Fruits legumes, oblong to linear, tapered asymmetrically to a sharply pointed or more commonly beaked tip, flattened or in a few species turgid, not or only slightly constricted between the seeds, straight or slightly curved upward, 2- to numerous-seeded, dehiscing by 2 valves, these green to brown at maturity, usually twisting spirally after dehiscence. Seeds oblong to kidney-shaped, nearly circular or somewhat angular in outline, flattened or not, the surface smooth or wrinkled, olive brown to dark brown, sometimes mottled. About 160 species, nearly worldwide, most diverse in temperate regions.

Lathyrus is a member of the tribe Fabeae, which is one of the most economically important groups in the family and also includes the related genera Lens Mill. (lentil), Pisum L. (garden pea), and Vicia L. (vetch). Species of Lathyrus are widely planted for soil cover, green manure, and occasionally for human food. The seeds of L. sativus L. (grass pea) are high in protein and it has been cultivated for at least 8,000 years (Smartt, 1990). They are highly drought resistant and produce a crop when other crops fail completely. The use of the species as food for humans and fodder for livestock is limited by the presence of toxic nonprotein amino acids that cause a syndrome known as lathyrism, one of the oldest neurotoxic diseases known (Burrows and Tyrl, 2001). Symptoms include spasms, weakness, paralysis of the legs, and ultimately muscular atrophy. Lathyrism remains a problem in impoverished countries where people are forced to subsist on Lathyrus peas for lengthy periods in times of famine. Curiously, the evolution and divergence of Lathyrus species has been accompanied by a threefold increase in chromosome size and fourfold increase in the amount of DNA (Narayan, 1982; Nandini et al., 1997).